Heterogeneous computer system, heterogeneous input/output system and data back-up method for the systems

ABSTRACT

A heterogeneous computer system, a heterogeneous input/output system and a data back-up method for the systems. An I/O subsystem A for open system and an I/O subsystem B for a mainframe are connected by a communication unit. In order to back up the data from at least a disk connected to the I/O subsystem B in a MT library system and in order to permit the mainframe to access the data in the I/O subsystem B, the I/O subsystem A includes a table for assigning a vacant memory address in a local subsystem to the memory of the I/O subsystem for an open system. A request of variable-length record format received from the mainframe is converted into a fixed-length record format for the subsystem B. The disk designated according to the table is accessed, and the data thus obtained is sent to the mainframe and backed up in the back-up system.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a division of application Ser. No. 10/326,978filed on Dec. 24, 2002, which is a continuation of application Ser. No.09/594,012 filed on Jun. 15, 2000, now U.S. Pat. No. 6,529,976, which isa continuation of application Ser. No. 09/052,985 filed on Apr. 1, 1998,now U.S. Pat. No. 6,098,129. The contents of application Ser. Nos.10/326,978, 09/594,012 and 09/052,985 are hereby incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a heterogeneous computer systemcomprising a host computer and a plurality of I/O subsystems, and morein particular to a method for making it possible to back up the datastored in a memory between a host computer and an I/O subsystem whichcannot be directly connected due to the difference in access interface,and a heterogeneous computer system including a plurality of I/Osubsystems having different access interfaces connected to the systemand the host computer.

[0003] In mainframes, a large scale of memory hierarchy (storagehierarchy) including a combination of a plurality of external memorieshaving different processing speeds and different storage capacities isaccompanied by a satisfactory data management function and an overallstorage management function intended to support an optimum dataarrangement and an efficient operation. The IBM's DFSMS (Data FacilityStorage Management Subsystem) is an example, which is described indetail in “IBM SYSTEMS JOURNAL, Vol. 28, No. 1, 1989, pp. 77-103.

[0004] The disk data of the I/O subsystem of the mainframe computersystem having the above-mentioned management function can be backed upin a medium such as a magnetic tape or a magnetic tape library capableof storing a large quantity of data with a low cost per bit.

[0005] An open system such as a personal computer or a work station,unlike the mainframe, is not equipped with a magnetic tape or a magnetictape library capable of storing a large quantity of data.

[0006] Generally, in an open system such as a personal computer or awork station, a disk is accessed in accordance with a fixed-lengthrecord format, while the mainframe accesses a disk in accordance with avariable-length record format called the count key data format.

[0007] As a result, the disk subsystem for the mainframe computer isoften configured independently of the disk subsystem for the opensystem. On the other hand, a technique for transmitting and receivingdata between I/O subsystems is disclosed in U.S. Pat. No. 5,155,845.

[0008] In a disk subsystem for an open system and a disk subsystem for amainframe computer which use different host computers, the back-up andother functions are independently operated and managed.

[0009] In view of the fact that the open system lacks a medium such as amagnetic tape or a magnetic tape library capable of storing a largerquantity of data, as described above, it is effective to back up thedata in the I/O subsystem of the mainframe.

[0010] An ordinary disk system for the open system, however, cannot beconnected directly to the mainframe due to the difference in theinterface thereof.

[0011] U.S. Pat. No. 5,155,845 fails to disclose how to process theread/write operation for a storage system not directly connected to ahost computer.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide a method and asystem for backing up data stored in a memory between a host computerand an I/O subsystem that cannot be connected directly to each other dueto the difference in access interface.

[0013] Specifically, an object of the invention is to provide a methodand a system for backing up data stored in an I/O subsystem of an opensystem from a mainframe not directly connected to the I/O subsystem.

[0014] Another object of the invention is to provide a method and acomputer system in which a mainframe is capable of accessing a memory ofan I/O subsystem of an open system not directly connected to themainframe.

[0015] Still another object of the invention is to provide a system anda method of access in which two or more I/O subsystems having differentinterfaces can be connected to a mainframe.

[0016] In order to achieve the above-mentioned objects, according to oneaspect of the present invention, there is provided a heterogeneouscomputer system comprising a first host computer, a first I/O subsystemdirectly connected to the first host computer by an interface ofvariable-length record format and including at least one externalmemory, a second host computer, a second I/O subsystem directlyconnected to the second host computer by an interface of fixed-lengthrecord format and including at least one external memory, and acommunication unit for connecting the first I/O subsystem to the secondI/O subsystem;

[0017] wherein the first I/O subsystem includes a table for storing adevice address of an external memory, data indicating one of theexternal memory of the first I/O subsystem and the external memory ofthe second I/O subsystem to which the device address is assigned, and adevice address of the external memory in the second I/O subsystem whenthe device address is assigned to the external memory of the second I/Osubsystem; and

[0018] wherein upon receipt of a read/write request conforming to theinterface of variable-length record format from the first host computerand including an address of an external memory to be read from orwritten into, and upon decision, with reference to the table, that theexternal memory address included in the read/write request is assignedto the external memory included in the second I/O subsystem, the firstI/O subsystem converts the read/write request into a second read/writerequest conforming to the interface of fixed-length record format andsends the second read/write request to the second I/O subsystem.

[0019] According to another aspect of the invention, there is provided aheterogeneous computer system comprising a first host computer, a firstI/O subsystem directly connected to the first host computer by aninterface of variable-length record format and including at least oneexternal memory, a back-up system connected to the first host computer,a second host computer, a second I/O subsystem directly connected to thesecond host computer by an interface of fixed-length record format andincluding at least one external memory, and a communication unit forconnecting the first I/O subsystem to the second I/O subsystem;

[0020] wherein the first host computer includes a means for issuing tothe first I/O subsystem a read request conforming to the interface ofvariable-length record format and containing the address of an externalmemory from which data is to be read, and backing up the data receivedfrom the first l/o subsystem into the back-up system;

[0021] wherein the first I/O subsystem includes a table for storing thedevice address of an external memory, data indicating that one of theexternal memory of the first and the second I/O subsystems to which thedevice address is assigned, and the device address of the externalmemory in the second I/O subsystem when the first device address isassigned to the external memory of the second I/o subsystem; and

[0022] wherein upon receipt from the first host computer of a readrequest conforming to the interface of variable-length record formatincluding an external memory address to be read, and upon decision, withreference to the above-mentioned table, that the device address of thememory address included in the read request is assigned to the externalmemory included in the second I/O subsystem, the first I/O subsystemconverts the read request into a second read request conforming to thefixed-length interface and sends the second read request to the secondI/O subsystem while at the same time sending to the first host computerthe data received from the second I/O subsystem.

[0023] According to still another aspect of the invention, there isprovided a heterogeneous computer system comprising a first hostcomputer, a first I/O subsystem directly connected to the first hostcomputer by an interface of variable-length record format and includingat least one external memory, a back-up system connected to the firsthost computer, a second host computer, a second I/O subsystem directlyconnected to the second host computer by an interface of fixed-lengthrecord format and including at least one external memory, and acommunication unit for connecting the first I/O subsystem to the secondI/O subsystem;

[0024] wherein the first host computer includes a means for issuing tothe first I/O subsystem a write request conforming to the interface ofvariable-length record format including the address of an externalmemory into which data is to be written, and sending the data read fromthe back-up system to the first I/O subsystem;

[0025] wherein the first I/O subsystem includes a table for storing thedevice address of an external memory, data indicating that one of theexternal memory of the first and the second I/O subsystems to which thedevice address is assigned, and the device address of the externalmemory in the second I/O subsystem when the first device address isassigned to the external memory of the second I/O subsystem; and

[0026] wherein upon receipt from the first host computer of a readrequest conforming to the interface of variable-length record formatincluding the device address an external memory to be written into, andupon decision, with reference to the table, that the address of theexternal memory included in the write request is assigned to theexternal memory included in the second I/O subsystem, the first I/Osubsystem converts the write request into a second write requestconforming to the interface of fixed-length record format, sends thesecond read request to the second I/O subsystem while at the same timesending the data received from the first host computer to the second I/Osubsystem.

[0027] According to yet another aspect of the invention, there isprovided a heterogeneous I/O system for use with a host, computerconnected thereto, comprising a first I/O subsystem including at leastone external memory, and a second I/O subsystem connected to the firstI/O subsystem and including at least one external memory;

[0028] wherein the first I/O subsystem includes a table for storing adevice address of an external memory, data indicating one of theexternal memories of the first and the second 110 subsystems to whichthe device address is assigned, and a device address of the externalmemory in the second I/O subsystem when the first device address isassigned to the external memory of the second I/O subsystem;

[0029] wherein upon receipt of a read/write request designating thedevice address of an external memory to be read from or written into bythe host computer, and upon decision, with reference to the table, thatthe external memory address in the designated address is assigned to theexternal memory included in the second I/O subsystem, the first I/Osubsystem sends the read/write request to the second I/O subsystem.

[0030] According to a further aspect of the invention, there is provideda heterogeneous I/O system for use with a host computer connectedthereto, comprising a first I/O subsystem having an interface ofvariable-length record format and including at least one externalmemory, a second I/O subsystem having an interface of fixed-lengthrecord format and including at least one external memory, and acommunication unit for connecting the first I/O subsystem to the secondI/O subsystem;

[0031] wherein the first I/O subsystem includes a table for storing adevice address of an external memory, data indicating one of theexternal memories of the first and the second I/O subsystems to whichthe device address is assigned, and a device address of the externalmemory in the second I/O subsystem when the first device address isassigned to the external memory of the second I/O subsystem; and

[0032] wherein upon receipt from the host computer of a read/writerequest conforming to the interface of variable-length record formatincluding the address of an external memory to be read from or writteninto, and upon decision, with reference to the table, that the externalmemory address included in the read/write request is assigned to theexternal memory included in the second I/O subsystem, the first I/Osubsystem converts the read/write request into a second read/writerequest conforming to the interface of fixed-length record format andsends it to the second I/O subsystem.

[0033] According to an embodiment of the invention, there is provided aheterogeneous computer system, wherein an I/O subsystem for an opensystem is connected to an I/O subsystem for a mainframe by acommunication unit, wherein, in order to access data in the I/Osubsystem for an open system from the mainframe for enabling the data inthe disk connected to the I/O subsystem for the open system to be backedup in a magnetic tape library system; a table is prepared for assigninga vacant address of the memory in the local subsystem to the memory ofthe I/O subsystem for the open system, wherein a request ofvariable-length record format received from the mainframe is convertedinto a request of fixed-length record format for the open system;wherein the disk designated according to the table is accessed, andwherein the data thus obtained is sent to the mainframe and backed up inthe back-up system.

[0034] This configuration can back up the data of an I/O subsystem foran open system in a back-up system under the management of a mainframenot directly connected to the particular I/O subsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is a block diagram showing a configuration of aheterogeneous computer system according to an embodiment of the presentinvention.

[0036]FIG. 2 is a block diagram showing a configuration of aheterogeneous computer system according to another embodiment of theinvention.

[0037]FIG. 3 is a block diagram showing a configuration of a diskcontroller of the heterogeneous computer system shown in FIGS. 1 and 2.

[0038]FIG. 4 is a diagram showing a configuration of a localcontroller-connected disk data (table) for the systems shown in FIGS. 1and 2.

[0039]FIG. 5 is a diagram showing a configuration of a remotecontroller-connected disk data (table) for the systems shown in FIGS. 1and 2.

[0040]FIG. 6 is a diagram showing the interconnection of disk devices asviewed from the mainframe.

[0041]FIG. 7 is a diagram showing an example of the processing flow of adisk controller A in the case where the data in an I/O subsystem for anopen system is backed up in an MT library system of the mainframe.

[0042]FIG. 8 is a diagram showing an example of the processing flow of adisk controller A in the case where data are restored in an I/Osubsystem for an open system from an MT library system of the mainframe.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Embodiments of the invention will be described below withreference to the accompanying drawings.

[0044]FIG. 1 is a diagram showing a configuration of a computer systemaccording to an embodiment of the invention.

[0045] A processing system A 100 includes a mainframe 101, a channelinterface A 102, a channel interface B 103, a magnetic tape (MT)controller 106, a magnetic tape library controller 130, a magnetic tapelibrary 107, a disk controller A 104, a disk drive group A 105 and aservice processor A 109. A back-up processing device 162 and a restoreprocessing device 164 are mounted on the mainframe 101.

[0046] The mainframe 101 accesses the disk controller A 104 through thechannel interface B 103 conforming with a variable-length record formatcalled the count-key-data format.

[0047] The count-key-data format is a record format in which a recordconstituting a unit of read/write operation is configured of threefields including a count field, a key field and a data field.

[0048] A record ID is stored in the count field, a key data foraccessing the record is stored in the key field, and the data used by anapplication program is stored in the data field.

[0049] In the description that follows, the magnetic tape (MT)controller 106, the magnetic tape library controller 130 and themagnetic tape library 107 are collectively referred to as an MT librarysystem 116. The disk controller A 104 and the disk drive group A 105constitute an I/O subsystem 10 connected to the mainframe 101. Insimilar fashion, the disk controller B 113 and the disk drive group B114 constitute an I/O subsystem 20 connected to a host 111 for an opensystem.

[0050] An optical disk or the like, as well as a magnetic disk,constitutes a rank of storage hierarchy connected through the channelinterface. The following description refers to the case in which the MTlibrary system 116 is connected. The disk controller A 104 containslocal controller-connected disk data 314 and remote controller-connecteddisk data 315.

[0051] The local controller-connected disk data 314 and the remotecontroller-connected disk data 315 are data provided for making itpossible for the mainframe to access a disk device of the I/O subsystemnot directly connected thereto. Specifically, the data 314 and 415 are atable for assigning a vacant address of the memory in the local I/Osubsystem for the processing system A to the memory of the I/O subsystemfor the open system so that the data in the I/O subsystem 20 for theprocessing system B can be accessed from the mainframe 101. The data 314and 315 will be described in detail later.

[0052] The processing system B 110 includes a host 111 for the opensystem, a SCSI (small computer system interface) 112, the diskcontroller B 113, the disk drive group B 114 and a service processor B115.

[0053] The host 111 for the open system accesses the disk controller B113 through the SCSI 112 having a fixed-length record which is a unit ofread/write operation.

[0054] The disk controller A 104 and the disk controller B 113 areconnected by a communication line 108. The communication line 108 canbe, for example, a SCSI cable B 117.

[0055] In the description that follows, the count-key-data format willbe called the CKD format, and the fixed-length block format will becalled an FBA (fixed block architecture) format.

[0056] Also, the record of the CKD format will be referred to as the CKDrecord, and the record of the FBA format will be referred to as the FBArecord.

[0057]FIG. 2 is a diagram showing another example of a computer systemaccording to the invention, in which a single I/O subsystem, for themainframe is connected to two or more I/O subsystems for an open system.

[0058] In a processing system X 120, the interfaces of an open systemhost X 121 and a disk controller X 123 are connected to each other by afiber channel interface 122. The fiber channel interface 122 is anoptical fiber cable which can increase the length of connection betweena host and a control device.

[0059] In many case, however, a fiber channel interface based on SCSI isemployed between a host and a control device.

[0060] Also, an interface such as a fiber channel interface X 126 can beused to connect a disk controller X 123 and the disk controller B 113.

[0061] The data back-up system in the configuration of FIG. 2 is anexpansion of the data back-up system in the configuration of FIG. 1.

[0062] The fundamental operation of each system is such that themainframe 101 and the hosts 111 and 121 for the open system access themagnetic tape library 107 constituting an external memory or the diskdrive group A 105, the disk drive group B 114 and the disk drive group X124 through each interface.

[0063] The process in the mainframe 101 establishes a route to the datastored externally through each interface under the control of anarbitrary operating system such as Hitachi's VOS3 (virtual-storageoperating system 3) for supporting the channel interface, while theprocess in the host for the open system establishes a route to theexternally-stored data through each interface under the control of anarbitrary operating system such as UNIX (a registered trade mark ownedby X/Open in U.S.A. and other countries) for supporting the SCSI.

[0064]FIG. 3 is a diagram showing a configuration of the disk controllerA 104. The disk controller A 104 includes a MPU 302 for executing acontrol system process 307 of the disk controller, a memory 301, a hostdata transfer device 303, a disk/cache device 304, an inter-I/Osubsystem data transfer device 305, a data transfer device 306 and acontrol bus 308 for connecting these devices.

[0065] The control system process 307 operates in a multitask ormultiprocessor environment.

[0066] The memory 301 includes various microprograms 312 and variousdata 313.

[0067] Especially, the disk controller A 104 has stored therein thelocal controller-connected data 314 and the remote controller-connecteddisk data 315, as described above with reference to FIG. 1.

[0068] The disk controller B 113 and the disk controller X 123 have aconfiguration similar to the disk controller A 104 and will not bedescribed in detail.

[0069] The disk controller B 113 and the disk controller X 123, however,are not required to contain the local controller-connected disk data 314and the remote controller-connected disk data 315.

[0070] The local controller-connected disk data 314 is the dataindicating the connections of the controllers and the like, and storedin the memory 301 of the disk controller A 104. The localcontroller-connected disk data 314 exists as the data corresponding toeach disk device.

[0071] The local controller-connected disk data 314 is shown in FIG. 4.

[0072] The device address 400 is an identifier (ID) for discriminating adisk device to be read from or written into by a host computer such asthe mainframe 101, and is the data also contained in the read/writerequest issued by the host computer such as the mainframe 101.

[0073] Local controller connection data 401 is the 25 data indicatingwhether or not the disk drive corresponding to the controller-connecteddisk data 314 is actually connected to a controller.

[0074] A remote controller connection pointer 402 indicates whether ornot the controller-connected disk data 314 is assigned to a disk driveconnected to a remote controller.

[0075] In the case where the such data is assigned to a disk driveconnected to a remote controller, the pointer indicates a correspondingremote controller-connected disk data 315. Otherwise, the pointerassumes a null value.

[0076] In the case where the remote controller connection pointer 402 isvalid (i.e. in the case where the particular device address 400 isassigned to a disk device connected to a remote controller), itrepresents the state in which the local controller connection data 401is not assigned.

[0077] In the case where the remote controller connection pointer 402 isinvalid (i.e. in the case where the device address 400 is not assignedto a disk drive connected to a remote controller), on the other hand,the local controller connection data 401 may indicate the state ofno-assignment.

[0078] In other words, the device address 400 may be assigned to neithera disk device connected to a local controller nor a disk deviceconnected to a remote controller.

[0079] An attribute 403 is the data unique to a device including theinterface, the function, the data format and the block length of thedisk drive.

[0080] The local controller-connected disk data 315 shown in FIG. 5 isthe data corresponding to a disk drive not directly connected to thedisk controller A 104.

[0081] It follows therefore that the remote controller-connected diskdata 315, on the other hand, is pointed to by any one of the localcontroller-connected disk data 314.

[0082] A connection controller address 500 represents the address of acontroller connected with a disk device corresponding to the remotecontroller-connected disk data 315. According to this embodiment, theaddress of the disk controller B 113 is stored as the connectioncontroller address 500.

[0083] A disk address 501 represents the address assigned in thecontroller actually connected to a corresponding disk drive.

[0084] The local controller-connected disk data 314 and the remotecontroller-connected disk data 315 are set from the service processor109.

[0085] According to this embodiment, the mainframe 101 recognizes thatthe disk drive group B 114 (disks C and D) is also connected to the diskcontroller A 104 through the disk controller B 113, as shown in FIG. 6,taking advantage of the local controller-connected disk data 314 and theremote controller-connected disk data 315 shown in FIGS. 4 and 5.

[0086] This is because of the fact that the vacant address of disk driveavailable in the disk controller A 104 is assigned by the diskcontroller A 104 to a disk drive of the I/O subsystem for an opensystem.

[0087] Now, the back-up processing will be described with reference toFIGS. 1, 7 and 8.

[0088] Specifically, in FIG. 1 the back-up process 162 on the mainframe101 causes the data in the disk device group B 114 of the open system ofthe processing system B to be backed up in the MT library system 116through the disk controller A 104 and the mainframe 101 of theprocessing system A.

[0089] Conversely, the data backed up in the MT library system 116 isrestored in the disk drive group B 114 of the open system of theprocessing system B through the mainframe 101 and the disk controller A104 of the processing system A.

[0090] The back-up operation and the restoration described above areexecuted in response to a command from the mainframe 101.

[0091] First, an explanation will be given of the case in which the datain the disk drive group B 114 of the open system for the processingsystem B is backed up in the MT library system 116 through the diskcontroller A 104 and the mainframe 101 of the processing system A.

[0092] As already described above, the mainframe 101 has recognized thatthe disk drive group B 114 (disks C and D) are also connected to thedisk drive A 104. Therefore, the operation of the mainframe 101, whichis simply to issue a read request to the disk controller A 104 and backup the received data in the MT library system 116, will not be describedspecifically.

[0093] In the case of backing up data into the MT library system 116,the mainframe 101 issues a read request to the disk controller A 104.The disk controller A 104 executes the process in accordance with theflowchart of FIG. 7 in response to a read request from the mainframe101.

[0094] First, step 700 finds out a corresponding localcontroller-connected disk data 314 from the address of the disk drivedesignated in the read request.

[0095] Step 701 checks whether the designated disk drive is connected tothe disk controller A 104 or not.

[0096] In the case where the disk drive is connected to the diskcontroller A 104, step 702 reads the corresponding data from theparticular disk drive.

[0097] In the case where the disk drive is not connected to the diskcontroller A 104, in contrast, step 703 checks whether the designateddisk drive is connected to a remote disk controller (disk controller B113). In other words, it checks whether the remote controller connectionpointer 402 assumes a null value.

[0098] In the case where the check result shows that the remotecontroller connection pointer 402 assumes a null value indicating thatthe designated disk drive is not connected to the remote diskcontroller, an error is reported in step 704.

[0099] The operation specifically related to the invention isrepresented by step 705 and subsequent steps executed in the case wherea designated disk drive is connected to a remote disk controller (diskcontroller B 113).

[0100] First, in the case where the check result shows that the remotecontroller connection pointer 402 does not assume the null valueindicating that the designated disk drive is connected to a remote diskcontroller, step 705 finds out the remote controller-connected disk data315 corresponding to the designated disk drive based on the remotecontroller connection pointer 402. Then, the address of the diskcontroller (disk controller B 113) actually connected to the designateddisk drive and the address of the disk drive in the disk drive group Bconnected to the particular disk controller B 113 are acquired on thebasis of the remote controller-connected disk data 315 found as above.

[0101] Then, step 706 converts the address of the data to be read whichhas been received in the read request into the format of the disk driveconnected to the disk controller B 113.

[0102] In a read/write request from the mainframe 101, the address ofdata to be read or written is normally designated by the cylindernumber, the head number and the record number according to the CKDformat.

[0103] The record address expressed by the cylinder number, the headnumber and the record number will hereinafter be called CCHHR.

[0104] The disk drive connected to the disk controller B 113, on theother hand, has an access interface designated by LBA (logical blockaddress) in accordance with the FBA format.

[0105] Consequently, step 706 converts the access address of the data tobe read from CKD format to FBA format.

[0106] The conversion formula is given, for example, by

LBA=(CC×number of heads+HH)×track length+record number×record length

[0107] According to this embodiment, the disk controller A 104 and thedisk controller B 113 may have the same interface, in which case theconversion of the input/output interface format is not required.

[0108] Step 707 issues a request to the disk controller B 113 to readthe data from the area of the corresponding disk drive calculated instep 706.

[0109] Step 708 waits for the arrival of the requested data from thedisk controller B 113.

[0110] Step 709 sends the data received from the disk controller B 113to the main frame 101 thereby to complete the process.

[0111] The disk controller B 113 simply reads the data requested by thedisk controller A 104 from a disk drive, and sends it to the diskcontroller A 104. This process, therefore, is not described specificallyin the processing flow.

[0112] Next, an explanation will be given of a case in which data backedup in the MT library system 116 is restored by the restore process 164on the mainframe 101 in the disk drive group B 114 of the open system ofthe processing system B through the disk controller A 104 and themainframe 101 of the processing system A.

[0113] As described already above, the mainframe 101 has recognized thatthe disk drive group B 113. (disks C and D) are also connected to thedisk controller A 104.

[0114] Therefore, no explanation will be given of the operation of themainframe 101 which is simply to issue a write request to the diskcontroller A 104 to write the data read from the MT library system 116.

[0115] Upon receipt of a write request from the mainframe 101, the diskcontroller A 104 executes the process in accordance with the flowchartof FIG. 8.

[0116] In the processing flow of FIG. 8, steps 800 to 801, 803 to 806are similar to steps 700 to 701, 703 to 706 in FIG. 7, respectively, andtherefore will not be explained. Also, step 802 is normally the writeoperation, since the request from the mainframe 101 is a write request.Only the parts different from FIG. 7 will be described below.

[0117] Step 807 issues a request to the disk controller B 113 to writedata in the area of the corresponding disk drive calculated in step 807.

[0118] Next, in step 808, the write data is received from the mainframe101 and sent to the disk controller B 113.

[0119] Then, step 809 waits for a report on the completion of the writerequest from the disk controller B 113, and upon receipt of thecompletion report, sends it to the mainframe 101 thereby to complete theprocess.

[0120] The disk controller B 113 simply reads the data requested by thedisk controller A 104 from the corresponding disk drive and sends it tothe disk controller A 104. The related processing flow, therefore, isnot shown specifically.

[0121] The foregoing description concerns a system for backing up dataof the disk drive group B 114 of the open system of the processingsystem B by the processing system A. As another embodiment, aheterogeneous I/O subsystem can be configured in which only the diskcontroller B and the disk drive group B are connected to the processingsystem A and the mainframe is connected with two I/O subsystems havingdifferent interfaces. In such a case, three or more instead of two I/Osubsystems can be connected.

[0122] The above-mentioned embodiment permits data to be backed upbetween I/O subsystems having different access interfaces.

[0123] As a result, data stored in an I/O subsystem for an open systemcan be backed up into an I/O subsystem for the mainframe.

[0124] Also, the back-up mechanism of the mainframe includes alarge-capacity, high-performance and high-reliability MT library system.The data of the I/O subsystem for an open system, therefore, can bebacked up by a mainframe back-up mechanism high in performance andreliability.

[0125] Further, different I/O subsystems can be connected to themainframe.

What is claimed is:
 1. A storage system comprising: a disk controllercoupled to a host computer; a plurality of disks coupled to said diskcontroller; wherein said storage system is coupled to another storagesystem, and wherein said disk controller receives an I/O request fromsaid host computer, selects a storage system, in which a storage areaaccessed by said host computer exists, based on a disk address includedin said I/O request, and sends said I/O request to said another storagesystem if said storage area exists in said another storage system.
 2. Astorage system as claimed in claim 1, wherein said I/O request is awrite request to write data into said storage area.
 3. A storage systemas claimed in claim 1, wherein said disk controller comprises a memory,wherein corresponding information between a disk address and a storagesystem, in which a storage area designated by said disk address exists,is stored in said memory, and wherein said disk controller selects astorage system, in which said storage area accessed by said hostcomputer exists, using said corresponding information and said diskaddress included in said I/O request.
 4. A storage system as claimed inclaim 1, wherein said I/O request further includes a data address,wherein said disk address designates a disk recognized by said hostcomputer and said data address designates a storage area in a diskdesignated by said disk address, and wherein said disk controllerselects a storage system, in which an storage area accessed by said hostcomputer exists, not using said data address.
 5. A storage system asclaimed in claim 4, wherein said data address is a record ID.